Plasma processing chamber with dual axial gas injection and exhaust

ABSTRACT

An electrode is exposed to a plasma generation volume and is defined to transmit radiofrequency power to the plasma generation volume, and includes an upper surface for holding a substrate in exposure to the plasma generation volume. A gas distribution unit is disposed above the plasma generation volume and in a substantially parallel orientation to the electrode. The gas distribution unit includes an arrangement of gas supply ports for directing an input flow of a plasma process gas into the plasma generation volume in a direction substantially perpendicular to the upper surface of the electrode. The gas distribution unit also includes an arrangement of through-holes that each extend through the gas distribution unit to fluidly connect the plasma generation volume to an exhaust region. Each of the through-holes directs an exhaust flow from the plasma generation volume in a direction substantially perpendicular to the upper surface of the electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No.12/850,559, filed on even date herewith, entitled “Dual Plasma VolumeProcessing Apparatus for Neutral/Ion Flux Control.” The disclosure ofthe above-identified related application is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

As semiconductor feature sizes continue to get smaller, semiconductorfabrication processes struggle to keep pace. One type of fabricationprocess involves exposure of a semiconductor wafer to a plasma or otherfoam of reactant gas to either deposit material on the wafer or removematerial from the wafer. Smaller feature sizes demand more accuratematerial deposition and etching control, which in turn requires moreaccurate control of how the wafer is exposed to the plasma/reactant gas.These more accurate control requirements may include more accuratecontrol of plasma uniformity across the wafer, more accurate control ofplasma density across the wafer, and/or more accurate control of plasmaresidence time in exposure to the wafer, among others. It is in thiscontext that the present invention is created.

SUMMARY OF THE INVENTION

In one embodiment, a semiconductor wafer processing apparatus isdisclosed to include an electrode and a gas distribution unit. Theelectrode is exposed to a plasma generation volume and is defined totransmit radiofrequency (RF) power to the plasma generation volume. Theelectrode has an upper surface defined to hold a substrate in exposureto the plasma generation volume. The gas distribution unit is disposedabove the plasma generation volume and in a substantially parallelorientation with respect to the electrode. The gas distribution unit isdefined to include an arrangement of gas supply ports defined to directan input flow of a plasma process gas into the plasma generation volumein a direction substantially perpendicular to the upper surface of theelectrode. The gas distribution unit is further defined to include anarrangement of through-holes that each extend through the gasdistribution unit to fluidly connect the plasma generation volume to anexhaust region. Each of the through-holes is defined to direct anexhaust flow of the plasma process gas from the plasma generation volumein a direction substantially perpendicular to the upper surface of theelectrode.

In another embodiment, a system for semiconductor wafer processing isdisclosed. The system includes a chamber defined to have an interiorcavity. The system also includes a chuck disposed within the interiorcavity of the chamber. The chuck has an upper surface defined to hold asubstrate in exposure to a plasma generation volume. And, the chuck isdefined to supply RF power to the plasma generation volume. The systemalso includes an outer peripheral structure disposed on the chuck anddefined to surround and enclose a perimeter of the plasma generationvolume. The system further includes a gas distribution unit disposed onthe outer peripheral structure and defined to extend across the plasmageneration volume in a substantially parallel relationship to the uppersurface of the chuck. The gas distribution unit is defined to include anarrangement of gas supply ports defined to direct an input flow of aplasma process gas into the plasma generation volume. The gasdistribution unit is further defined to include an arrangement ofthrough-holes. The system also includes an exhaust region defined withinthe chamber above the gas distribution unit, such that each of thethrough-holes extends through the gas distribution unit to fluidlyconnect the plasma generation volume to the exhaust region. The systemalso includes a pump fluidly connected to the exhaust region to removegases from the exhaust region.

In another embodiment, a method is disclosed for semiconductor waferprocessing. The method includes an operation for holding a semiconductorwafer in a substantially parallel orientation to a gas distributionunit, such that a plasma processing volume is formed between thesemiconductor wafer and the gas distribution unit. The method alsoincludes an operation for flowing a plasma processing gas from withinthe gas distribution unit into the plasma processing volume in adirection substantially perpendicular to the semiconductor wafer. Themethod further includes an operation for directing an exhaust flow ofplasma processing gas from within the plasma processing volume throughthe gas distribution unit in a direction substantially perpendicular tothe semiconductor wafer, whereby the exhaust flow of plasma processinggas through the gas distribution unit is the only exhaust flow of plasmaprocessing gas from within the plasma processing volume.

Other aspects and advantages of the invention will become more apparentfrom the following detailed description, taken in conjunction with theaccompanying drawings, illustrating by way of example the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a semiconductor wafer processing apparatus, in accordancewith one embodiment of the present invention;

FIG. 1B shows the chamber of FIG. 1A with arrows depicting gas flow andexhaust flow through the gas distribution unit, in accordance with oneembodiment of the present invention;

FIG. 2 shows an alternative configuration of the chamber of FIG. 1A, inaccordance with one embodiment of the present invention;

FIG. 3A shows a bottom view of the gas distribution unit, in accordancewith one embodiment of the present invention;

FIG. 3B shows a top view of the gas distribution unit, in accordancewith one embodiment of the present invention;

FIG. 3C shows a gas supply port cross-section, in accordance with oneembodiment of the present invention;

FIG. 4A shows a flow control plate disposed on the upper surface of thegas distribution unit, in accordance with one embodiment of the presentinvention;

FIG. 4B shows a top view of the flow control plate positioned such thata hole pattern defined therein allows for flow through all through-holesdefined within the underlying gas distribution unit, in accordance withone embodiment of the present invention;

FIG. 4C shows a top view of the flow control plate positioned such thatthe hole pattern defined therein allows for flow through only a portionof the through-holes defined within the underlying gas distributionunit, in accordance with one embodiment of the present invention;

FIG. 4D shows a top view of a flow control plate assembly defined by anumber of concentric rotatable flow control plates, in accordance withone embodiment of the present invention; and

FIG. 5 shows a flowchart of a method for semiconductor wafer processing,in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the present invention. Itwill be apparent, however, to one skilled in the art that the presentinvention may be practiced without some or all of these specificdetails. In other instances, well known process operations have not beendescribed in detail in order not to unnecessarily obscure the presentinvention.

A semiconductor wafer processing apparatus is disclosed herein to enableprecise control of plasma residence time and uniformity across a waferto enable wafer fabrication processes that require rapid and uniformprocess gas injection and pump out. Examples of such wafer fabricationprocesses that require rapid and uniform process gas injection and pumpout include, but are not limited to, atomic layer etching and atomiclayer deposition.

The apparatus includes a gas distribution unit disposed above the plasmageneration region, with the wafer held on an electrostatic chuck belowand in exposure to the plasma generation region. The gas distributionunit is defined to supply the plasma process gas downward toward thewafer in a substantially uniform manner. The gas distribution unit isalso defined to exhaust plasma process gas upward from the wafer in asubstantially uniform manner. Thus, as described in more detail below,the gas distribution unit provides for both axial gas injection andexhaust.

FIG. 1A shows a semiconductor wafer processing apparatus, in accordancewith one embodiment of the present invention. The apparatus includes achamber 100 formed by a top plate 100A, a bottom plate 100B, and walls100C. In one embodiment, the walls 100C form a contiguous cylindricalshaped wall 100C. In other embodiments, the walls 100C can have otherconfigurations, so long as an interior cavity 100D of the chamber 100can be isolated from an external environment outside the chamber 100. Anumber of seals 139 are disposed between the chamber top plate 100A,bottom plate 100B, and walls 100C to facilitate isolation of theinterior cavity 100D of the chamber 100 from the external environment.

In various embodiments, the top plate 100A, bottom plate 100B, and walls100C of the chamber 100 can be formed of a metal that is a goodconductor of electricity and heat, and that is chemically compatiblewith the process gases to which the interior cavity 100D is to beexposed during wafer processing. For example, in various embodiments,metals such as aluminum, stainless steel, or the like, maybe used toform the chamber 100 components. Also, the seals 139 can be elastomericseals or consumable metallic seals, or any other type of seal material,so long as the seals 139 are chemically compatible with processingmaterials to which the interior cavity 100D will be exposed, and so longas the seals 139 provide sufficient isolation of the interior cavity100D from the external environment outside the chamber 100.

It should be appreciated that in other embodiments, one or moreadditional plates or members can be disposed outside any one or more ofthe top plate 100A, bottom plate 100B, or walls 100C, as necessary tosatisfy chamber 100 deployment-specific conditions or otherconsiderations. Additionally, the top plate 100A, bottom plate 100B,and/or walls 100C can be fastened to these additional plates or membersas appropriate for the particular implementation. The chamber 100structure, including the top plate 100A, bottom plate 100B and walls100C, is formed of an electrically conducting material and iselectrically connected to a reference ground potential.

The chamber 100 includes an exhaust port 135 which provides for fluidconnection of the interior cavity 100D to an external exhaust pump 137,such that a negative pressure can be applied through the exhaust port135 to remove gases and/or particulates from within the interior cavity100D. In one embodiment, the chamber 100 also includes a gate valve 102formed within a section of the chamber wall 100C to enable insertion ofa wafer 113 into the interior cavity 100D, and corresponding removal ofthe wafer 113 from the interior cavity 100D. In its closed position, thegate valve 102 is defined to maintain isolation of the interior cavity100D from the external environment. In various embodiments, the exhaustpump 137 can be implemented in different ways, so long as the exhaustpump 137 is capable of applying a suction at the exhaust port 135 todraw a fluid flow from the interior cavity 100D of the chamber 100.

A plasma processing apparatus is disposed within the interior cavity100D of the chamber 100. The plasma processing apparatus includes aplasma generation volume 109 formed between a chuck 107A/B and a gasdistribution unit 115. More specifically, the plasma generation volume109 resides above the chuck 107A/B and below the gas distribution unit115, with an upper surface of the chuck 107A/B and a lower surface ofthe gas distribution unit 115 disposed in a substantially parallelorientation with respect to each other. A peripheral structural member108 is also disposed to enclose a perimeter of the plasma generationvolume 109 between the gas distribution unit 115 and the upper surfaceof the chuck 107A/B.

As mentioned above, the chuck 107A/B is disposed within the interiorcavity 100D of the chamber 100 below the plasma generation volume 109.The chuck 107A/B includes a body portion 107A and an electrode portion107B In one embodiment, the chuck body 107A is cantilevered from thewall 100C of the chamber 100. In one embodiment, the chuck 107A/B is anelectrostatic chuck with the electrode 107B defined to transmit RF powerto the plasma generation volume 109. An upper surface of the electrodeportion of the chuck 107B is defined to hold a substrate 113, i.e.,wafer 113, in exposure to the plasma generation volume 109. In oneembodiment, a quartz focus ring 149 is disposed on the body of the chuck107A about the periphery of a substrate 113 receiving/holding area onthe chuck 107B. The chuck 107 is also defined to include a configurationof cooling channels and/or heating elements, so as to enable temperaturecontrol of the substrate 113 and the plasma generation volume 109.

The chuck 107A/B is defined to move vertically within the interiorcavity 100D, as indicated by arrows 123. In this manner, the chuck107A/B can be lowered to receive/provide the substrate 113 through thegate valve 102, and can be raised to form the lower surface of theplasma generation volume 109. Also, a vertical distance across theplasma generation volume 109, as measured perpendicular to both thechuck 107B and the gas distribution unit 115, can be set and controlledby controlling the vertical position of the chuck 107B. The verticaldistance across the plasma generation volume 109 can be set to achieve asufficient center-to-edge plasma uniformity and density, and can also beset to avoid printing on the wafer 113 by jets of gas flowing from gassupply ports 119 of the gas distribution unit 115. In variousembodiments, the vertical distance across the plasma generation volume109 can be set within a range extending from about 1 cm to about 5 cm.In one embodiment, the vertical distance across the plasma generationvolume 109 is set at about 2 cm. It should be appreciated that thevertical distance across the plasma generation volume 109 is controlledto enable rapid evacuation of the plasma generation volume 109, andthereby enable accurate control of plasma residence time within theplasma generation volume 109.

The electrode portion of the chuck 107B is defined to supply RF powerfrom an RF power source 111 to the plasma generation volume 109. Itshould be understood that the RF power source 111 is connected through amatching network to enable transmission of the RF power to the electrodeportion of the chuck 107B. As previously discussed, in one embodiment,the gas distribution unit 115 is electrically connected to a referenceground potential, such that the gas distribution unit 115 serves as areference ground electrode in the RF power return path for the plasmageneration volumes 109.

The gas distribution unit 115 is held in a fixed position above theplasma generation volume 109 and the peripheral structural member 108.The gas distribution unit 115 is defined to supply a plasma process gasto the plasma generation volume 109 through an arrangement of gas supplyports 119. The gas distribution unit 115 is further defined to includean arrangement of through-holes 117 to provide for fluid exhaust fromthe plasma generation volume 109. Each of the through-holes 117 extendsthrough the gas distribution unit 115 plate from its upper surface toits lower surface.

FIG. 1B shows the chamber 100 of FIG. 1A with arrows depicting gas flowand exhaust flow through the gas distribution unit 115, in accordancewith one embodiment of the present invention. As shown in FIGS. 1A and1B, plasma process gas is supplied to the gas distribution unit 115 fromone or more plasma process gas supply sources 118A/118B. The plasmaprocess gas flows through the gas distribution unit 115 and out of thegas supply ports 119 into the plasma generation volume 109. The plasmaprocess gas is exhausted from the plasma generation volume 109 throughthe through-holes 117 of the gas distribution unit 115 into a exhaustmanifold 103. In the embodiment of FIGS. 1A and 1B, the plasmageneration volume 109 is sealed such that plasma process gas is onlyexhausted through the through-holes 117 of the gas distribution unit 115into the exhaust manifold 103.

In one embodiment, the exhaust manifold 103 is connected to a vacuumpump 102, by way of a valve 101. The valve 101 can be operated tofluidly connect/disconnect the exhaust manifold 103 to/from the pump102, thereby enabling the pressure within the exhaust manifold 103 to bereleased to the pump 102, such that plasma process gas within the higherpressure plasma generation volume 109 will flow through thethrough-holes 117 of the gas distribution unit 115, into the lowerpressure exhaust manifold 103, through the valve 101, to the pump 102,so as to exhaust the plasma process gas from the plasma generationvolume 109.

FIG. 2 shows an alternative configuration of the chamber 100, inaccordance with one embodiment of the present invention. In thisembodiment, the through-holes 117 of the gas distribution unit 115 arein fluid communication with the interior cavity 100D of the chamber 100.In this embodiment, plasma process gas is exhausted from the plasmageneration volume 109 through the through-holes 117 of the gasdistribution unit 115 directly into the interior cavity 100D of thechamber 100. The plasma process gas within the interior cavity 100D ofthe chamber is removed through the exhaust port 135, by way of the pump137. In this embodiment, the interior cavity 100D of the chamber 100serves as the exhaust manifold. Thus, the outer structural member 104 ofthe embodiment of FIGS. 1A and 1B is removed. And, the top plate 100A isreplaced by a top plate 100E that does not include the valve 101 and theconnection to the pump 102. In this embodiment, the pressure within theinterior cavity 100D of the chamber 100 can be controlled relative tothe pressure within the plasma generation volume 109 to in turn controlthe plasma process gas exhaust flow rate through the through-holes 117of the gas distribution unit 115.

It should be appreciated that the dual axial plasma process gas inputand exhaust provided by the gas distribution unit 115 enables plasmaprocessing of the wafer 113 with substantially uniform center-to-edgeplasma density over the wafer 113. More specifically, the dual axialplasma process gas input and exhaust provided by the gas distributionunit 115 prevents radial plasma process gas flows within the plasmageneration volume 109, which could cause radial non-uniformity in thecenter-to-edge plasma density profile. Also, the dual axial plasmaprocess gas input and exhaust provided by the gas distribution unit 115enables plasma processing of the wafer 113 with substantially shortplasma residence time on the wafer 113, when necessary.

FIG. 3A shows a bottom view of the gas distribution unit 115, inaccordance with one embodiment of the present invention. Each of the gassupply ports 119 and through-holes 117 are defined in open fluidcommunication through the lower surface of the gas distribution unit115. The arrangement of gas supply ports 119 is interspersed between thearrangement of through-holes 117. The gas supply ports 119 are plumbedthrough the gas distribution unit 115 to one or more plasma process gassupply sources 118A/B, such that no direct fluid communication existsbetween the gas supply ports 119 and the through-holes 117 within thegas distribution unit 115.

FIG. 3B shows a top view of the gas distribution unit 115, in accordancewith one embodiment of the present invention. Each of the through-holes117 is defined in open fluid communication through the upper surface ofthe gas distribution unit 115. However, the gas supply ports 119 are notfluidly exposed through the upper surface of the gas distribution unit115. Therefore, the gas supply ports 119 are defined to flow plasmaprocess gas into only the plasma generation volume 109. In contrast, thethrough-holes 117 are defined to enable fluid communication from theplasma generation volume 109 to the exhaust manifold 103 (or to theinterior cavity 100D in the embodiment of FIG. 2). Fluid flow throughthe through-holes 117 of the gas distribution unit 115 is controlledprimarily by a pressure differential between the plasma generationvolume 109 and the exhaust manifold 103 (or the interior cavity 100D inthe embodiment of FIG. 2).

It should be understood that the gas distribution unit 115 serves as aRF return path electrode, plasma process gas manifold, and fluid flowbaffle plate. In various embodiments the gas distribution unit 115 canbe formed of metal that is a good conductor of electricity and heat, andthat is chemically compatible with the processes to be conducted in theplasma generation volume 109, such as aluminum, stainless steel, or thelike. In various embodiments, the gas distribution unit 115 can beelectrically connected to either a reference ground potential or a biasvoltage to enable the RF return path electrode function of the gasdistribution unit 115. Thus, the gas distribution unit 115 provides aground electrode for the plasma generation volume 109. In oneembodiment, the electrode 107B and the gas distribution unit 115 form anapproximate one-to-one power-to-ground surface area. The configurationof the gas distribution unit 115 relative to the electrode 107B enablesformation of a capacitively coupled plasma within the plasma generationvolume 109.

In one embodiment, portions of the gas distribution unit 115 that areexposed to plasma are protected by a covering of plasma resistantmaterial. In one embodiment, the plasma resistant material is formed asa coating. In another embodiment, the plasma resistant material isformed as a protective structure, e.g., plate, that conformally coversthe gas distribution unit 115. In either of these embodiments, theplasma resistant material is secured to the gas distribution unit 115 toensure adequate electrical and thermal conduction between the plasmaresistant material and the gas distribution unit 115. In the embodimentof the plasma resistant protective structure, the protective structuremay be secured to the gas distribution unit 115 by a number offasteners, or by compression between the gas distribution unit 115 andthe outer peripheral structure 108 when disposed beneath the gasdistribution unit 115. In various embodiments, the plasma resistantcoating/protective structure used to protect the gas distribution unit115 can be formed of silicone, silicon carbide, silicon oxide, yttriumoxide, or essentially any other material that provides adequate plasmaresistance, electrical conduction, and thermal conduction for the plasmaprocesses to which it is exposed.

The gas distribution unit 115 is defined as a swappable component.Different versions/configurations of the gas distribution unit 115 canbe defined to have different arrangements of the gas supply ports 119and through-holes 117. Additionally, in the event that plasmadeteriorates the gas distribution unit 115 or its functionality, the gasdistribution unit 115 can be replaced.

Each of the gas supply ports 119 and through-holes 117 is defined tooptimize fluid flow through it, while simultaneously preventing adverseintrusion of plasma into it. Fluid flow and plasma intrusionthrough/into each of the gas supply ports 119 and though-holes 117 isdirectly proportional to its size. Therefore, it is necessary to defineeach of the gas supply ports 119 and though-holes 117 such that its sizeis small enough to prevent adverse plasma intrusion into it, whileremaining large enough to provide adequate fluid flow through it. Invarious embodiments, the diameter of the gas supply ports 119 is sizedwithin a range extending from about 0.1 mm to about 3 mm. In variousembodiments, the diameter of the through-holes 117 is sized within arange extending from about 0.5 mm to about 5 mm. It should beunderstood, however, that in various embodiments the gas supply ports119 and through-holes 117 can be respectively defined with essentiallyany diameter size, so long as the diameter size provides for adequatefluid flow there through while simultaneously providing for adequatesuppression of plasma intrusion therein.

Because the fluid flow pressure to the gas supply ports 119 is directlycontrollable, it is possible to define the gas supply ports 119 to havea small enough size to essentially prevent plasma intrusion into the gassupply ports 119. However, it is appropriate to avoid defining the gassupply ports 119 so small as to cause supersonic fluid flow through thegas supply ports 119. To avoid supersonic fluid flow from the gas supplyports 119, the gas supply ports 119 can be defined to have a diffusershape at their exit from the lower surface of the gas distribution unit115. FIG. 3C shows a gas supply port 119 cross-section, in accordancewith one embodiment of the present invention. The gas supply port 119 isshown to have a diffuser shape 307 at its exit location from the gasdistribution unit 115.

The gas distribution unit 115 includes interior gas supply channelsfluidly connected to the arrangement of gas supply ports 119. Theseinterior gas supply channels are fluidly connected to one or more plasmaprocess gas supply sources 118A/B. Although the embodiments of FIGS. 1A,1B, and 2 show two plasma process gas supply sources 118A/B for ease ofdescription, it should be understood that essentially any number ofplasma process gas supply sources 118A/B/C/D, etc., can be connected tosupply plasma process gas to the gas distribution unit 115, depending onthe specific configuration of the gas distribution unit 115 and chamber100. Also, it should be understood that the interior gas supply channelsand associated gas supply ports 119 are defined between the arrangementof through-holes 117 such that the plasma process gas is distributed tothe plasma generation volume 109 before entering the through-holes 117.

In one embodiment, such as depicted in FIG. 3A, the interior gas supplychannels within the gas distribution unit 115 are defined to fluidlyseparate the arrangement of gas supply ports 119 into multipleconcentric regions/zones 115A, 115B, 115C across the lower surface ofthe gas distribution unit 115, such that flow rates of the plasmaprocess gas to the gas supply ports 119 within each of the multipleconcentric regions/zones 115A, 115B, 115C can be separately controlled.In one embodiment, the gas supply ports 119 within each concentricradial region/zone 115A, 115B, 115C are plumbed to a respective gas flowcontrol device 305A, 305B, 305C, such that supply of the plasma processgas to each concentric radial region/zone 115A, 115B, 115C isindependently controllable.

Separation of the gas supply ports 119 into independently controllablemultiple concentric regions/zones 115A, 115B, 115C provides forcenter-to-edge gas supply control within the plasma generation volume109, which in turn improves center-to-edge plasma uniformity controlwithin the plasma generation volume 109. Although the example embodimentof FIG. 3A shows three concentric gas supply regions/zones 115A, 115B,115C, it should be understood that the gas distribution unit 115 can bedefined to include more or less independently controllable gas supplyregions/zones. For example, in another embodiment, the gas distributionunit 115 is defined to include two independently controllable concentricgas supply regions/zones.

In one embodiment, the number of through-holes 117 is greater than thenumber gas supply ports 119, to provide for adequate fluid exhaust flowfrom the plasma generation volume 109. Also, the through-holes 117 canbe defined to have a larger size than the gas supply ports 119, toprovide for adequate fluid exhaust flow from the plasma generationvolume 109. However, as previously discussed, the size of thethrough-holes 117 is limited to prevent adverse plasma intrusion fromthe plasma generation volume 109 into the through-holes 117.

In one embodiment, a flow control plate is disposed on the upper surfaceof the gas distribution unit 115 to control which through-holes 117 areopen for fluid exhaust from the plasma generation volume 109. FIG. 4Ashows a flow control plate 401 disposed on the upper surface 302 of thegas distribution unit 115, in accordance with one embodiment of thepresent invention. In one embodiment, the flow control plate 401 isdefined as a disc having a thickness 403 within a range extending fromabout 3 mm to about 6 mm. The flow control plate 401 disc is defined tohave a diameter sufficient to cover the through-holes 117 through whichflow is to be controlled. In one embodiment, the flow control plate 401disc is defined to have a diameter that covers the upper surface of thegas distribution unit 115.

In one embodiment, the flow control plate 401 is formed of anelectrically and thermally conductive material, and is secured to thegas distribution unit 115 to ensure adequate electrical and thermalconduction between the flow control plate 401 and the gas distributionunit 115. In one embodiment, the flow control plate 401 is secured tothe gas distribution unit 115 by a number of fasteners. Also, in variousembodiments, the flow control plate 401 can be covered and protected bya plasma resistant coating such as that discussed above with regard tothe gas distribution unit 115.

In one embodiment, multiple patterns of holes are defined through theflow control plate 401. Each of the multiple patterns of holes withinthe flow control plate 401 aligns with a different set of through-holes117 within the gas distribution unit 115. Disposal of the flow controlplate 401 on the upper surface of the gas distribution unit 115 at aparticular rotational position of the flow control plate 401 relative tothe upper surface of the gas distribution unit 115 corresponds toalignment of a particular one of the multiple patterns of holes withinthe flow control plate 401 with its corresponding set of through-holes117 within the gas distribution unit 115. Each of the multiple patternsof holes that extends through the flow control plate 401 is defined toexpose a different number or a different spatial pattern ofthrough-holes 117 within the gas distribution unit 115. Therefore, fluidexhaust through the gas distribution unit 115 can be controlled bysetting the flow control plate 401 at a particular rotational positionrelative to the upper surface of the gas distribution unit 115.

FIG. 4B shows a top view of the flow control plate 401 positioned suchthat a hole 405 pattern defined therein allows for flow through allthrough-holes 117 defined within the underlying gas distribution unit115, in accordance with one embodiment of the present invention. FIG. 4Cshows a top view of the flow control plate 401 positioned such that thehole 405 pattern defined therein allows for flow through only a portionof the through-holes 117 defined within the underlying gas distributionunit 115, in accordance with one embodiment of the present invention.Also, in other embodiments, the multiple patterns of holes 405 in theflow control plate 401 are defined to provide for different spatialpatterns of fluid exhaust flow through the gas distribution unit 115.

FIG. 4D shows a top view of a flow control plate assembly 401A definedby a number of concentric rotatable flow control plates 407A, 407B,407C, in accordance with one embodiment of the present invention. Eachconcentric rotatable flow control plate 407A, 407B, 407C can be setindependently to provide center-to-edge control over which through-holes117 are open or closed within the gas distribution unit 117.Specifically, the flow control plate assembly 401A includes a centraldisc 407A and a number of concentric rings 407B/407C, disposed in aconcentric manner on the upper surface of the gas distribution unit 115.It should be understood that the particular configuration of FIG. 4D isprovided by way of example. Other embodiments may include a differentnumber of concentric rotatable flow control plates than what is shown inFIG. 4D.

Each of the central disc 407A and the number of concentric rings407B/407C respectively include multiple patterns of holes extendingthere through. Each of the multiple patterns of holes aligns with adifferent set of through-holes 117 within the gas distribution unit 115,such that disposal of each of the central disc 407A and the concentricrings 407B/407C on the upper surface of the gas distribution unit 115,at a particular rotational position relative to the upper surface of thegas distribution unit 115, corresponds to alignment of a particular oneof the multiple patterns of holes with its corresponding set ofthrough-holes 117 within the gas distribution unit 115. Each of themultiple patterns of holes extending through the central disc 407A andthe concentric rings 407B/407C is defined to expose a different numberor a different spatial pattern of through-holes 117 within the gasdistribution unit 115.

It should be understood that plasma generation volume 109 is sized tocontain a confined plasma. A confined plasma is beneficial in that itsresidence time can be controlled by controlling volume, pressure, andflow within the plasma region, i.e., within the plasma generation volume109. Plasma residence time affects the dissociation process, which is afactor in radical/neutron formation. Also, plasma residence time affectsan amount of deposition or etching that occurs on the wafer 113, whichis an important factor in performing short residence time processes suchas atomic layer deposition or atomic layer etching. The plasmageneration volume 109 is small and well-controlled with regard topressure and temperature. In various embodiments, a pressure within thelower plasma processing volume 109 can be controlled within a rangeextending from about 5 mTorr to about 100 mTorr, or from about 10 mTorrto about 30 mTorr, or from about 100 mTorr to about 1 Torr, or fromabout 200 mTorr to about 600 mTorr.

It should be appreciated that the dual axial plasma process gas inputand exhaust provided by the gas distribution unit 115 enables accuratepressure uniformity control across the wafer 113, because gases arepumped out vertically as opposed to radially, which would cause a radialpressure distribution across wafer 113. The dual axial plasma processgas input and exhaust also allows for accurate control of residence timein low flow applications, such as atomic layer deposition or atomiclayer etching in which short plasma residence time, e.g., less than amillisecond, is required.

FIG. 5 shows a flowchart of a method for semiconductor wafer processing,in accordance with one embodiment of the present invention. The methodincludes an operation 501 for holding a semiconductor wafer in asubstantially parallel orientation to a gas distribution unit, such thata plasma processing volume is formed between the semiconductor wafer andthe gas distribution unit. In one embodiment, the gas distribution unitis defined as a plate that extends over an entirety of the plasmaprocessing volume. Also, in one embodiment, the semiconductor wafer isheld on an upper surface of a chuck. The method also includes anoperation 503 for flowing a plasma processing gas from within the gasdistribution unit into the plasma processing volume in a directionsubstantially perpendicular to the semiconductor wafer. Additionally, anoperation 505 is performed to direct an exhaust flow of plasmaprocessing gas from within the plasma processing volume through the gasdistribution unit in a direction substantially perpendicular to thesemiconductor wafer. The exhaust flow of plasma processing gas throughthe gas distribution unit is the only exhaust flow of plasma processinggas from within the plasma processing volume.

The method further includes an operation 507 for transmitting RF powerto the plasma processing volume to transform the plasma processing gasinto a plasma in exposure to the semiconductor wafer. In one embodiment,the chuck that holds the semiconductor wafer is operated as an electrodeto transmit the RF power to the plasma processing volume. Also in themethod, the exhaust flow of plasma processing gas from the gasdistribution unit is received into an exhaust region. A pump is operatedto provide a suction force to a valve fluidly connected to the exhaustregion. And, the valve is operated to control an exhaust flow out of theexhaust region, and thereby control the exhaust flow from the plasmageneration volume through the gas distribution unit into the exhaustregion.

In one embodiment, operation 503 includes flowing the plasma processinggas from multiple independently controllable gas supply zones within thegas distribution unit into the plasma processing volume. In thisembodiment, respective flow rates of plasma processing gas through eachof the multiple gas supply zones are controlled to enable control aplasma density across the semiconductor wafer. Also, in oneimplementation of this embodiment, the multiple independentlycontrollable gas supply zones are concentrically defined across the gasdistribution unit. Additionally, in one embodiment, flowing the plasmaprocessing gas from within the gas distribution unit into the plasmaprocessing volume, and directing the exhaust flow of plasma processinggas from within the plasma processing volume through the gasdistribution unit, are performed in a pulsed manner to control aresidence time of plasma in exposure to the semiconductor wafer.

While this invention has been described in terms of several embodiments,it will be appreciated that those skilled in the art upon reading thepreceding specifications and studying the drawings will realize variousalterations, additions, permutations and equivalents thereof. It istherefore intended that the present invention includes all suchalterations, additions, permutations, and equivalents as fall within thetrue spirit and scope of the invention.

What is claimed is:
 1. A semiconductor wafer processing apparatus,comprising: a chuck including an electrode exposed to a plasmageneration volume, the electrode defined to transmit radiofrequency (RF)power to the plasma generation volume, the electrode having an uppersurface defined to hold a substrate in exposure to the plasma generationvolume, the chuck having a top surface that circumscribes a perimeter ofa top surface of the electrode; and a gas distribution unit disposedabove the plasma generation volume and in a substantially parallelorientation with respect to the electrode, the gas distribution unitdefined to include an arrangement of gas supply ports defined to directan input flow of a plasma process gas into the plasma generation volumein a direction substantially perpendicular to the upper surface of theelectrode, the gas distribution unit further defined to include anarrangement of through-holes that each extend through the gasdistribution unit to fluidly connect the plasma generation volume to anexhaust region, wherein each of the through-holes is defined to directan exhaust flow of the plasma process gas from the plasma generationvolume in a direction substantially perpendicular to the upper surfaceof the electrode, and wherein the gas distribution unit is defined as aplate formed to separate the plasma generation volume from the exhaustregion, and wherein each gas supply port in the arrangement of gassupply ports is defined at a lower surface of the plate to provide fordistribution of plasma process gas to the plasma generation volume; anouter peripheral structure having a top surface and a bottom surface andformed to extend in a solid form between its top and bottom surfaces,the bottom surface of the outer peripheral structure disposed on the topsurface of the chuck, the gas distribution unit disposed on the topsurface of the outer peripheral structure, the outer peripheralstructure defined to surround and enclose a perimeter of the plasmageneration volume such that an uninterrupted fluid seal is presentbetween the bottom surface of the outer peripheral structure and the topsurface of the chuck around the perimeter of the plasma generationvolume, and such that an uninterrupted fluid seal is present between thetop surface of the outer peripheral structure and the gas distributionunit around the perimeter of the plasma generation volume.
 2. Thesemiconductor wafer processing apparatus as recited in claim 1, whereinthe electrode forms a lower surface of the plasma generation volume, andwherein a lower surface of the plate provides an upper boundary of theplasma generation volume.
 3. The semiconductor wafer processingapparatus as recited in claim 1, wherein the gas distribution unit isformed of an electrically conductive material and is electricallyconnected to a reference ground potential such that the gas distributionunit provides a ground electrode for the plasma generation volume. 4.The semiconductor wafer processing apparatus as recited in claim 1,wherein the electrode is movable in a direction toward and away from thegas distribution unit to provide for control of a distance extendingacross the plasma generation volume perpendicular to both the electrodeand gas distribution unit.
 5. The semiconductor wafer processingapparatus as recited in claim 1, further comprising: an exhaust manifolddisposed above the gas distribution unit to form the exhaust region; avalve fluidly connected to the exhaust manifold; and a pump fluidlyconnected to the valve to provide a suction force to the valve, whereinthe valve is operable to control an exhaust flow from the plasmageneration volume through the gas distribution unit.
 6. Thesemiconductor wafer processing apparatus as recited in claim 1, furthercomprising: a chamber defined to enclose the electrode and the gasdistribution unit within an interior cavity of the chamber, wherein theinterior cavity of the chamber forms the exhaust region; a pump fluidlyconnected to the interior cavity of the chamber to provide a suctionforce to the interior cavity of the chamber; and a valve disposed tocontrol a fluid flow from the interior cavity of the chamber due to thesuction force provided by the pump.
 7. A system for semiconductor waferprocessing, comprising: a chamber defined to have an interior cavity; achuck disposed within the interior cavity of the chamber, the chuckhaving an upper surface defined to hold a substrate in exposure to aplasma generation volume, the chuck defined to supply radiofrequency(RF) power to the plasma generation volume; an outer peripheralstructure disposed on the chuck and defined to surround and enclose aperimeter of the plasma generation volume such that an uninterruptedfluid seal is present between the outer peripheral structure and thechuck around the perimeter of the plasma generation volume; a gasdistribution unit disposed on the outer peripheral structure such thatan uninterrupted fluid seal is present between the outer peripheralstructure and the gas distribution unit around the perimeter of theplasma generation volume, the gas distribution unit defined to extendacross the plasma generation volume in a substantially parallelrelationship to the upper surface of the chuck, the gas distributionunit defined to include an arrangement of gas supply ports defined todirect an input flow of a plasma process gas into the plasma generationvolume, the gas distribution unit further defined to include anarrangement of through-holes; an exhaust region defined within thechamber above the gas distribution unit such that each of thethrough-holes extends through the gas distribution unit to fluidlyconnect the plasma generation volume to the exhaust region, wherein thearrangement of through-holes is an only means for exhausting gases fromthe plasma generation volume; and a pump fluidly connected to theexhaust region to remove gases from the exhaust region.
 8. The systemfor semiconductor wafer processing as recited in claim 7, wherein eachof the gas supply ports is defined to direct the input flow of theplasma process gas into the plasma generation volume in a directionsubstantially perpendicular to the upper surface of the chuck, andwherein each of the through-holes is defined to direct the exhaust flowof the plasma process gas from the plasma generation volume in adirection substantially perpendicular to the upper surface of the chuck.9. The system for semiconductor wafer processing as recited in claim 7,wherein the gas distribution unit is formed of an electricallyconductive material and is electrically connected to a reference groundpotential such that the gas distribution unit provides a groundelectrode for the plasma generation volume.
 10. The system forsemiconductor wafer processing as recited in claim 7, wherein the chuckis movable in a direction toward and away from the gas distribution unitto provide for control of a distance extending across the plasmageneration volume perpendicular to both the upper surface of the chuckand the gas distribution unit.
 11. The semiconductor wafer processingapparatus as recited in claim 1, further comprising: a flow controlplate disposed on an upper surface of the gas distribution unit, theflow control plate defined to control which of the through-holes areexposed to direct the exhaust flow of the plasma process gas from theplasma generation volume and which of the through-holes are closed at agiven time.
 12. The semiconductor wafer processing apparatus as recitedin claim 11, wherein the flow control plate is a disc having multiplepatterns of holes defined through the disc, such that each of themultiple patterns of holes aligns with a different set of thethrough-holes at a corresponding rotational position of the discrelative to the upper surface of the gas distribution unit.
 13. Thesemiconductor wafer processing apparatus as recited in claim 12, whereineach of the multiple patterns of holes is defined to expose a differentnumber or a different spatial pattern of the through-holes within thegas distribution unit.
 14. The system for semiconductor wafer processingas recited in claim 7, further comprising: a flow control plate disposedon an upper surface of the gas distribution unit, the flow control platedefined to control which of the through-holes are exposed to fluidlyconnect the plasma generation volume to the exhaust region and which ofthe through-holes are closed at a given time.
 15. The system forsemiconductor wafer processing as recited in claim 14, wherein the flowcontrol plate is a disc having multiple patterns of holes definedthrough the disc, such that each of the multiple patterns of holesaligns with a different set of the through-holes at a correspondingrotational position of the disc relative to the upper surface of the gasdistribution unit.
 16. The system for semiconductor wafer processing asrecited in claim 15, wherein each of the multiple patterns of holes isdefined to expose a different number or a different spatial pattern ofthe through-holes within the gas distribution unit.
 17. Thesemiconductor wafer processing apparatus as recited in claim 1, whereineach through-hole of the arrangement of through-holes is defined at thelower surface of the plate such that each through-hole is spaced apartfrom neighboring gas supply ports by some portion of the lower surfaceof the plate.
 18. The system for semiconductor wafer processing asrecited in claim 7, wherein the gas distribution unit is defined as aplate formed to separate the plasma generation volume from the exhaustregion, and wherein each gas supply port in the arrangement of gassupply ports is defined at a lower surface of the plate with a diffusershape to provide for distribution of plasma process gas to the plasmageneration volume.
 19. The system for semiconductor wafer processing asrecited in claim 18, wherein each through-hole of the arrangement ofthrough-holes is defined at the lower surface of the plate such thateach through-hole is spaced apart from neighboring gas supply ports bysome portion of the lower surface of the plate.
 20. The system forsemiconductor wafer processing as recited in claim 7, wherein the gasdistribution unit includes interior gas supply channels fluidlyconnected to the arrangement of gas supply ports, the interior gassupply channels defined to fluidly separate the arrangement of gassupply ports into multiple gas supply regions including a center gassupply region and one or more annular gas supply regions definedconcentrically about the center gas supply region across the gasdistribution unit such that each of the one or more annular gas supplyregions circumscribes the center gas supply region, the system includinga number of gas flow control devices corresponding to a number of themultiple gas supply regions into which the arrangement of gas supplyports is separated, wherein each gas supply port of a given one of themultiple gas supply regions is plumbed to a same gas flow controldevice, and wherein gas supply ports of different ones of the multiplegas supply regions are plumbed to different gas flow control devices toprovide for independent control of gas flow to the multiple gas supplyregions.
 21. The semiconductor wafer processing apparatus as recited inclaim 1, wherein the gas distribution unit includes interior gas supplychannels fluidly connected to the arrangement of gas supply ports, theinterior gas supply channels defined to fluidly separate the arrangementof gas supply ports into multiple gas supply regions including a centergas supply region and one or more annular gas supply regions definedconcentrically about the center gas supply region across the gasdistribution unit such that each of the one or more annular gas supplyregions circumscribes the center gas supply region, wherein each gassupply port of a given one of the multiple gas supply regions is plumbedto a same gas flow control device, and wherein gas supply ports ofdifferent ones of the multiple gas supply regions are plumbed todifferent gas flow control devices to provide for independent control ofgas flow to the multiple gas supply regions.